This application claims the benefit of Korean Patent Application No. 2000-48236, filed on Aug. 21, 2000, under 35 U.S.C. xc2xa7119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to reflective and transflective LCD devices having black resin.
2. Description of Related Art
Until now, the cathode-ray tube (CRT) has been developed and mainly used for display systems. However, flat panel displays are beginning to make an appearance because of their small depth dimensions, desirably low weight, and low voltage power supply requirements. Presently, thin film transistor-liquid crystal displays (TFT-LCDs) with high resolution and small depth dimension are being developed.
During operation of the TFT-LCD, a pixel is turned ON by switching elements to transmit light generated from a backlight device. The switching elements are generally amorphous silicon thin film transistors (a-Si:H TFTs) that use an amorphous silicon layer. Advantageously, the amorphous silicon TFTs can be formed on low cost glass substrates using low temperature processing techniques.
In general, the TFT-LCD transmits image data using light emitted from the backlight device that is positioned under a TFT-LCD panel. However, the TFT-LCD only employs 3xcx9c8% of the incident light generated from the backlight device, thereby providing inefficient optical modulation. In the TFT-LCD device, two polarizers will typically have a transmittance of 45% and two corresponding substrates will typically have a transmittance of 94%. The TFT array and the pixel electrode may have a transmittance of 65% and the color filter may have a transmittance of 27%. Therefore, the typical transmissive TFT-LCD device has a relative transmittance of about 7.4% as shown in FIG. 1. Additionally, FIG. 1 also shows the relative transmittance after light passes through each layer of the device. For this reason, the transmissive TFT-LCD device requires a light source having a relatively high initial brightness. However, such a high initial brightness increases electric power consumption requirements of the backlight device. Accordingly, a relatively heavy battery is needed to supply sufficient power to the backlight device. Moreover, use of the battery source will limit the time in which the TFT-LCD can properly operate.
In order to overcome these problems, a reflective TFT-LCD has been developed. Since the reflective TFT-LCD device uses ambient light as a light source, the device is light and portable. Additionally, the reflective TFT-LCD device has a superior aperture ratio as compared to a transmissive TFT-LCD device. Namely, since the reflective TFT-LCD substitutes an opaque reflective electrode for a transparent electrode material in the pixel of the conventional transmissive TFT-LCD, the opaque reflective electrode reflects ambient light. Accordingly, since the reflective TFT-LCD device uses ambient light rather than an internal light source, battery life of the reflective TFT-LCD can be increased resulting in a longer period of use. In other words, the reflective TFT-LCD device is driven using light reflected from the reflective electrode, thereby only drive circuitry that drives the liquid crystal uses the battery source in the reflective TFT-LCD device.
FIG. 2 is a schematic cross-sectional view of a conventional reflective liquid crystal display device. In FIG. 2, the reflective LCD device 20 comprises an upper substrate 2, a lower substrate 4, and a liquid crystal layer 3 interposed therebetween. On a first surface of the upper substrate 2 that opposes the lower substrate 4, a black matrix 6 isolates color filters 8 (Red, Green and Blue) that are disposed on the first surface of the upper substrate 2. The color filters 8 and the black matrix 6 are disposed on a similar plane, and a transparent common electrode 10 is disposed on the color filters 8 and black matrix 6.
A gate insulation layer 18 is disposed on a first surface of the lower substrate 4 that opposes the first surface of the upper substrate 2. A passivation layer 14 is disposed on the gate insulation layer 18, and data lines 16 that transmit data signals to the TFT (not shown) are disposed between the gate insulation layer 18 and the passivation layer 14 and on both sides of a pixel region. A reflective electrode 12 is disposed on the passivation layer 14 and, in combination with the transparent electrode 10, controls orientation of liquid crystal molecules 9 by application of an electric field. The reflective electrode 12 reflects ambient light to display image data and functions as a pixel electrode. Furthermore, since the reflective LCD device 20 displays image data using the ambient light, lateral side edges of the reflective electrode 12 overlap portions of the data lines 16, thereby increasing aperture ratio. The reflective electrode 12 is formed of an opaque metallic material that has superior light reflectance, while the passivation layer 14 is formed of an insulating material that has a low dielectric constant of about 3 (xcex5≈3), such as benzocyclobutene (BCB) or acryl-based resin, for example. Accordingly, since the passivation layer is disposed between the reflective electrode 12 and the data lines 16, electrical interference, i.e., cross talk, is prevented. Here, a thickness of the passivation layer 14 is about 1.5 micrometers (xcexcm).
In FIG. 2, an overlap area xe2x80x9cAxe2x80x9d represents an area of the pixel electrode 12 that overlaps the data line 16. Since the data line 16 is shielded from incident light by this overlap area xe2x80x9cAxe2x80x9d of the pixel electrode 12, a substantial portion of the black matrix 6 corresponding to the overlap area xe2x80x9cAxe2x80x9d can be removed. However, if the portion of the black matrix 6 corresponding to the overlap area xe2x80x9cAxe2x80x9d is removed, a width of the black matrix 6 is narrowed, thereby creating misalignment problems during manufacturing processes. For example, the misalignment of the red, green and blue color filters 8 is created due to a small aligning margin of the black matrix 6, and the misalignment of the upper and lower substrates is created when attaching the upper substrate 2 to the lower substrate 4. The width of the overlap area xe2x80x9cAxe2x80x9d is about 2 xcexcm, and a width of the black matrix is ideally about 4 xcexcm. However, in practice the ideal width of the black matrix is difficult to obtain because of the above-mentioned problems. Accordingly, a width of more than 4 xcexcm needs to be maintained for the black matrix so that the overlap area xe2x80x9cAxe2x80x9d is covered by the black matrix. Thus, increasing the aperture ratio is difficult.
Meanwhile, the reflective TFT-LCD device can be adversely affected by its surroundings. For example, the brightness of indoor ambient light differs greatly from the brightness of outdoor ambient light. In addition, the brightness of the outdoor ambient light is dependent upon the time of day (i.e., noon or dusk) such that the reflective TFT-LCD device cannot be used at night without sufficient ambient light. Accordingly, there is a need for a transflective TFT-LCD device that can be used during daylight hours, as well as nighttime, since the transflective LCD device can be changed to either a transmissive mode or a reflective mode depending on the desired condition of operation.
FIG. 3 is a schematic cross-sectional view of a pixel area of a conventional transflective liquid crystal display device. In FIG. 3, the transflective TFT-LCD device includes a liquid crystal panel 45 and a backlight device 44. The liquid crystal display panel 45 includes an upper substrate 22, a lower substrate 24 and a liquid crystal layer 31 interposed therebetween. The upper substrate 22 and the lower substrate 24 are commonly referred to as a color filter substrate and an array substrate, respectively. The upper substrate 22 includes a black matrix 26 and color filters 28 on a surface of the upper substrate 22 that faces the lower substrate 24, and a transparent common electrode 30 is formed on the color filters 28 and black matrix 26. Here, the black matrix 26 and color filters 28 are located in a common plane.
In FIG. 3, the lower substrate 24 has a gate insulation layer 33 disposed on a surface that faces the upper substrate 22 and data lines 34 are formed on the gate insulation layer 33. A passivation layer 32 is formed on the gate insulation layer 33 while covering the data lines 34 and has a trapezoidal-shaped transmitting hole 42. Thus, the passivation layer 32 has inclined portions disposed adjacent to the transmitting hole 42. A transparent electrode 36 is formed on the passivation layer 32 and is disposed within the transmitting hole 42, and an interlayer insulator 38 and a reflective electrode 40 are formed in series on the transparent electrode 36. The interlayer insulator 38 electrically insulates the reflective electrode 40 from the transparent electrode 36.
In the transflective liquid crystal display device described above, the reflective electrode 40 and the transparent electrode 36 function together as a pixel electrode. Furthermore, the lower substrate 24 is divided into a reflective portion xe2x80x9crxe2x80x9d and a transmitting portion xe2x80x9ctxe2x80x9d such that the passivation layer 32 is formed to create different cell gaps between the reflective portion xe2x80x9crxe2x80x9d and the transmitting portion xe2x80x9ct.xe2x80x9d Namely, a first cell gap is defined by an interval, i.e., the reflective portion, between the reflective electrode 40 and the transparent common electrode 30, and a second cell gap is defined by an interval, i.e., the transparent portion, between the transparent electrode 36 and the transparent common electrode 30. As shown in FIG. 3, the passivation layer 32 of the array substrate 24 is formed to create a step difference between the first cell gap and the second cell gap. Thus, the thickness of the liquid crystal layer 31 is different within each of the first and second cell gaps. Preferably, the second cell gap is twice as long as the first cell gap.
As previously described, the reflective electrode 40 in the reflective portion xe2x80x9crxe2x80x9d reflects the ambient light, while the transparent electrode 36 in the transmitting portion xe2x80x9ctxe2x80x9d transmits the light emitted from the backlight device 44. In this structure, the reflective electrode 40 overlaps a portion of the data line 34, thereby forming an overlap area xe2x80x9cE.xe2x80x9d The overlap area xe2x80x9cExe2x80x9d extends the pixel region and the aperture ratio similar to the reflective LCD device shown in FIG. 2. However, it is difficult to obtain a desired aperture ratio because a width of the black matrix 26 is required to be about 4 xcexcm. Moreover, as previously described, if a portion of the black matrix 26 corresponding to the overlap area xe2x80x9cExe2x80x9d is removed, the width of the black matrix 26 is narrowed, thereby creating misalignment problems during manufacturing processes. For example, the misalignment of the red, green and blue color filters 28 occurs due to a small alignment margin of the black matrix 26, and the misalignment of the upper and lower substrates occurs when attaching the upper substrate 22 to the lower substrate 24.
Furthermore, in the transflective LCD device shown in FIG. 3, portions of the reflective electrode 40 are positioned on the inclined portions of the interlayer insulator 38 to prevent light leakage. In addition, extended portions xe2x80x9cFxe2x80x9d of the reflective electrode 40 are disposed along a peripheral planar portion of the interlayer insulator 38 disposed within the transmitting hole 42. The extended portions xe2x80x9cFxe2x80x9d decrease a margin of the light leakage error. Therefore, the aperture ratio decreases because the extended portions xe2x80x9cFxe2x80x9d of the reflective electrode 40 cover a peripheral portion of the transmitting hole 42 in a transmissive mode of the transflective LCD device.
Accordingly, the present invention is directed to reflective and transflective liquid crystal display devices having black resin that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide reflective and transflective liquid crystal display devices with increased aperture ratios.
Another object of the present invention is to provide reflective and transflective liquid crystal display devices with improved manufacturing processes.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the liquid crystal display device includes first and second substrates facing and spaced apart from each other, a liquid crystal layer interposed between the first and second substrates, a transparent common electrode disposed on the first substrate, a gate line disposed on the second substrate along a first direction, a data line disposed on the second substrate along a second direction perpendicular to the first direction, a thin film transistor disposed at an intersection of the gate line and the data line, a gate insulation layer disposed on the second substrate, a black resin layer disposed on the gate insulation layer, and a reflective electrode disposed on the passivation layer, wherein the reflective electrode overlaps end portions of the data line.
In another aspect, the liquid crystal display device includes first and second substrates facing and spaced apart from each other, a liquid crystal layer interposed between the first and second substrates, a backlight device disposed adjacent to the second substrate for generating light, a transparent common electrode disposed on the first substrate, a gate line disposed on the second substrate along a first direction, a data line disposed on the second substrate along a second direction perpendicular to the first direction, a thin film transistor disposed at a crossing of the gate line and the data line, a gate insulation layer disposed on the second substrate, a passivation layer disposed on the gate insulation layer, the passivation layer having a transmitting hole extending to the gate insulation layer, and the passivation layer made of a black resin, a transparent electrode having a first portion disposed on the passivation layer and a second portion disposed within the transmitting hole, and a reflective electrode formed on the passivation layer, wherein the reflective electrode overlaps end portions of the data line.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.